Vaporization modeling of petroleum-biofuel drops using a hybrid multi-component approach

Numerical modeling of the vaporization characteristics of multi-component fuel mixtures is performed in this study. The fuel mixtures studied include those of binary components, biodiesel, diesel-biodiesel, and gasoline-ethanol. The use of biofuels has become increasingly important for reasons of environmental sustainability. Biofuels are often blended with petroleum fuels, and the detailed understanding of the vaporization process is essential to designing a clean and efficient combustion system. In this study, a hybrid vaporization model is developed that uses continuous thermodynamics to describe petroleum fuels and discrete components to represent biofuels. The model is validated using the experimental data of n-heptane, n-heptane-n-decane mixture, and biodiesel. Since biodiesel properties are not universal due to the variation in feedstock, methods for predicting biodiesel properties based on the five dominant fatty acid components are introduced. Good levels of agreement in the predicted and measured drop size histories are obtained. Furthermore, in modeling the diesel-biodiesel drop, results show that the drop lifetime increases with the biodiesel concentration in the blend. During vaporization, only the lighter components of diesel fuel vaporize at the beginning. Biodiesel components do not vaporize until some time during the vaporization process. On the other hand, results of gasoline-ethanol drops indicate that both fuels start to vaporize once the process begins. At the beginning, the lighter components of gasoline have a slightly higher vaporization rate than ethanol. After a certain time, ethanol vaporizes faster than the remaining gasoline components. At the end, the drop reduces to a regular gasoline drop with heavier components. Overall, the drop lifetime increases as the concentration of ethanol increases in the drop due to the higher latent heat.     

Thermodynamic modeling of partially stratified charge engine characteristics for hydrogen-methane blends at ultra-lean conditions

A thermodynamic model considering flame propagation is presented to predict SI engine characteristics for hydrogen-methane blends. The partially charge stratification approach which involves micro direct injection of pure fuel or a fuel–air mixture, to create a rich zone near the spark plug, is proposed as a method to improve engine performance. Presented approach was validated with experimental data for the natural gas at lean condition. The model was generalized to predict the performance of engine for a variety of hydrogen contents in hydrogen-methane blends. Hydrogen molar concentrations of 0%, 15%, 30%, and 45% were used in the simulations. Results showed that partially charge stratification improves engine performance by increasing indicated mean effective pressure and decreasing specific fuel consumption. The results indicated that increasing mole fraction of hydrogen content would improve the PSC effect on engine performance. An advantage of the presented model is the flexibility and simplicity that make it possible to investigate several effects such as mixture distribution and fuel constituents on engine performance more practical than other types of simulation.     

Auto-ignition of toluene-doped n-heptane and iso-octane/air mixtures: High-pressure shock-tube experiments and kinetics modeling

Toluene is often used as a fluorescent tracer for fuel concentration measurements, but without considering whether it affects the auto-ignition properties of the base fuel. We investigate the auto-ignition of pure toluene and its influence on the auto-ignition of n-heptane and iso-octane/air mixtures under engine-relevant conditions at typical tracer concentrations. Ignition delay times τ_ign were measured behind reflected shock waves in mixtures with air at φ = 1.0 and 0.5 at p = 40 bar, over a temperature range of T = 700–1200 K and compared to numerical results using two different mechanisms. Based on the models, information is derived about the relative influence of toluene on τ_ign on the base fuels as function of temperature. For typical toluene tracer concentrations ?10%, the ignition delay time τ_ign changes by less than 10% in the relevant pressure and temperature range.     

Visualization of hydrogen jet evolution and combustion under simulated direct-injection compression-ignition engine conditions

The evolution and combustion of H₂ jets were investigated in an optically-accessible constant-volume chamber under simulated direct-injection (DI) compression-ignition (CI) engine conditions. The parameters varied include injection pressure (84–140 bar) and ambient temperature (1000–1140 K). A detailed characterization of the injector system and the ensuing jet penetration process is reported first. High-speed schlieren imaging, OH1 chemiluminescence imaging and pressure trace measurements were subsequently used to investigate the auto-ignition and combustion of the H₂ jets. The results show that the ignition delay of H₂ jets under such conditions is sensitive to ambient temperature variations, but not to injection pressure. Optical imaging reveals that the combustion of H₂ jets mostly initiated from a localized kernel, before spreading to engulf the whole jet volume downstream of ignition location. The imaging also indicates that after ignition, the flame recesses back towards the nozzle and appears to attach to the nozzle to form a diffusion flame structure.     

An experimental investigation on engine performance and emissions of a single cylinder diesel engine using hydrogen as inducted fuel and diesel as injected fuel with exhaust gas recirculation

Fast depletion of fossil fuels is demanding an urgent need to carry out research work to find out the viable alternative fuels for meeting sustainable energy demand with minimum environmental impact. In the future, our energy systems will need to be renewable and sustainable, efficient and cost-effective, convenient and safe. The technology for producing hydrogen from a variety of resources, including renewable, is evolving and that will make hydrogen energy system as cost-effective. Hydrogen safety concerns are not the cause for fear but they simply are different than those we are accustomed to with gasoline, diesel and other fossil fuels. For the time being full substitution of diesel with hydrogen is not convenient but use of hydrogen in a diesel engine in dual fuel mode is possible. So Hydrogen has been proposed as the perfect fuel for this future energy system. The experiment is conducted using diesel–hydrogen blend. A timed manifold induction system which is electronically controlled has been developed to deliver hydrogen on to the intake manifold. The solenoid valve is activated by the new technique of taking signal from the rocker arm of the engine instead of cam actuation mechanism. In the present investigation hydrogen-enriched air has been used in a diesel engine with hydrogen flow rate at 0.15 kg/h. As diesel is substituted and hydrogen is inducted, the NO_x emission is increased. In order to reduce NO_x emission an EGR system has been developed. In the EGR system a lightweight EGR cooler has been used instead of bulky heat exchanger. In this experiment performance parameters such as brake thermal efficiency, volumetric efficiency, BSEC are determined and emissions such as oxides of nitrogen, carbon dioxide, carbon monoxide, hydrocarbon, smoke and exhaust gas temperature are measured. Dual fuel operation with hydrogen induction coupled with exhaust gas recirculation results in lowered emission level and improved performance level compared to the case of neat diesel operation.     

The behaviour of acetamide under ‘Galisol’ heat storage conditions

Acetamide, as a phase-change material for energy storage, is preferable to other organic materials because of its noncorrosive behaviour and the high storage capacity (264 MJ/m³). In the paper a possibility is offered for a considerable decrease of the supercooling tendency and for the prevention of the disturbing sublimation effects, by modifying the dynamic working function principle ‘Galisol’. For this purpose we have used a heat-transfer liquid with a partial solubility for acetamide. The study reviews solubility data, investigations of the thermal behaviour by the DTA method with large samples, cloud point investigations, equilibrium surface tensions and heat-storage investigations of combinations of acetamide and heat-transfer liquids. A phase diagram of the acetamide-trichloroethylene system is presented. The heat-storage behaviour of acetamide in its combination with trichloroethylene and a surface active material is very promising and offers a high heat-transfer power comparable to that of inorganic salt hydrates under ‘Galisol’ conditions. Nevertheless, the fact that water-free acetamide, which is very expensive, has to be used must be taken into consideration.     

Investigation and modeling of low cycle fatigue behaviors of two Ni-based superalloys under dwell conditions

The ability to predict fatigue behaviors of turbine-disk-materials under operating conditions is an important aspect of designing a safe turbine engine. Studies of two Ni-based superalloys, powder metallurgy (PM) FGH95 and Cast GH4169, have been undertaken to investigate their low cycle fatigue (LCF) behaviors with different dwell conditions reflecting the fatigue–creep interaction at high temperature of 650 °C. Based on the deformation behaviors obtained by the tests, the effects of dwell on mean stress and shape of hysteretic loop at half life have been analyzed and considered to be introduced in developing a new fatigue model. For the purpose, two groups of parameters are defined in order to introduce the effects of mean stress and shape of hysteretic loop, especially due to their changes caused by dwell. Finally, an energy-based fatigue model is given with modifying of the original energy-type damage parameter. As a comparison, four typical models of LCF are used to model the experimental results, which are the Strain Range Partitioning method (SRP), the Frequency Separation method (FS), the Damage Rate method (DR) and the Ostergren method. The experimental data of LCF of cast and wrought (CW) Rene95, and PM Rene95 from open resources are also used to verify abilities of the newly-developed model. The results show that the model can describe fatigue behaviors well, and the scatter bands are within ±2, even considering the dwell effects. The accuracy and adaptability of predicting LCF life of the model are better than those of the four existing models.     

A computational study and correlation of premixed isooctane–air laminar reaction front properties under spark ignited and spark assisted compression ignition engine conditions

To address the need for reliable premixed laminar burning velocity and thickness information within the spark assisted compression ignition (SACI) combustion regime, a large dataset of simulated reaction fronts has been generated in this work. A transient one dimensional premixed laminar flame simulation was applied to isooctane–air mixtures using a 215 species chemical kinetic mechanism. The simulation was exercised over fuel–air equivalence ratios, unburned gas temperatures and pressures ranging from 0.1 to 1.0, 298 to 1000 K and 1 to 250 bar, respectively, a range that extends beyond that of previous researchers. Steady reaction fronts with burning velocities in excess of 5 cm/s could not be established under all of these conditions, especially when burned gas temperatures were below 1500 K and/or when characteristic reaction front times were on the order of the unburned gas ignition delay. Steady premixed laminar burning velocities were correlated using a modified two-equation form based upon the asymptotic structure of a laminar flame, which produced an average error of 2.5% between the simulated and correlated laminar burning velocities, with a standard deviation of 3.0%. Additional correlations were constructed for reaction front thickness and adiabatic flame temperature. The resulting premixed laminar burning velocity correlation showed good agreement with experiments and existing correlations within the spark-ignited (SI) regime. Analysis of the simulated characteristic reaction front times and ignition delays suggests that homogeneous SACI combustion is most useful under medium and high load operating conditions.